38 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHRandom misfires... finally gone !
Reported repair
Replace cylinder 5 fuel injector
Reported resolution
1
Reported fixes
0
Unsuccessful attempts
1
Discussions
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Discussions that report a fix
1
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Reported fix
Finally they replaced the cylinder 5 fuel injector. No more misfires.
Leading evidence: 'Replace cylinder 5 fuel injector' (1 discussions report resolution; 0 report an unsuccessful attempt). Across 1 matching discussions, the most frequently mentioned possible cause is 'injector' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Replace cylinder 5 fuel injector' (1 discussions). For that action, 1 discussions report a resolution and 0 report an unsuccessful attempt. The most frequently reported fix is 'Replace cylinder 5 fuel injector', supported by resolution reports in 1 discussions. These are forum reports and suggestions, not a confirmed diagnosis.
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Reported cause
But the only thing that fixed it was the injector.
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Discussions that performed work without a confirmed outcome
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Performed · outcome unconfirmed · Original poster
I checked all connections to the throttle-body - good...
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Performed · outcome unconfirmed
Since I got the new engine installed, I personally replaced alternator, water pump with pier burg and two O2 sensors up and downstream on bank 1.
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Discussions that performed work without a confirmed outcome
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Performed · outcome unconfirmed
I also replaced my heater core, not too hard and I replaced my window cowl and one wiper spray nozzle.
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Suggestion · Original poster
I proceeded to check all grounds, and connections to both the coils and the injectors from the X51 connectors in the engine bay - they all checked out.
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Suspected cause
I suspect the reason is because these Porsches are very reliable, so when there IS a problem, we tend to think a part/component has failed, but because most parts are quite reliable, the connections become the failure point.
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
38 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
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Outcome without a verified action link
Anyway, I�m glad you got this resolved - good for you - being prudent and seeing it through.
... Wow! I basically spent the entire summer chasing (or trying to chase) these things down... I started by changing all 4 O2 sensors (had fault codes), the MAF (had code), CPS (no code, but apparently heat can affect operation. None of these had any good effect... The car would start and run fine until it got up to full operating temp. I proceeded to check all grounds, and connections to both the coils and the injectors from the X51 connectors in the engine bay - they all checked out. I checked all connections to the throttle-body - good... I always did one check at a time and then test drove the car to see if the misfires had gone away. Needless to say this was time consuming to say the least. In addition, I've been working on my house to prepare it for sale so time has been in short supply anyway. In addition, I wound up fixing/addressing a bunch of other little issues (like underbody rust, Front differential, underbody plastics, brake line to right rear wheel, etc...) while I had the car in the shop. At some point about 4-6 weeks ago I decided to break down and buy a set pf new coils as well as a set of injectors . While I didn't expect it to be the coils (due to the fact that the engine was rebuilt a little over a year ago and there's only about 10k on them - and I was trying not to "throw parts at it"), they're easier to change than the injectors so they got the nod first. Viola' ! Misfires are gone, the engine is running amazingly well again and the car has a bunch of little stuff sorted out - including the airbag light from when I changed the seats out (documented in this thread:
https://rennlist.com/forums/996-foru...a-996-a-4.html
). I'm pretty ecstatic, and am planning a nice trip to Woodstock/Bethel NY next weekend...
Bad coils for sure. I went through all the connections and they were all good. The big question is why all the coils went bad in such a short period of time??? Visually speaking, they look perfect...
^^ Yes - Beru coils. The newer/larger ones with the longer bolts. Again, no signs of cracking, arcing etc. they look perfect - I'm wondering if there's a funky batch floating around out there...
What I find more baffling is that all of them went bad at what seems to be the same time. One or two showing random misfires for awhile (always on the same cylinder) would have seemed more normal to me. I guess I just don't know enough about how the ignition system/ECU works - maybe one coil misfiring causes the others to misfire as well...
Did you check the coil ground points? There are grounds at each head on opposite ends, one on front side, one on rear side. If the coil ground is bad it can cause coils to fail early due to overheating !!!
I did. While I had the engine lowered I went in and cleaned them up as well. Unfortunately, I guess the coils were already damaged so whatever I had done to the grounds didn't show me any love...*** Great point for anyone who runs into this problem in the future!
Not a Euro Or Porsche specific thing, just a commonly overlooked cause of weird or intermittent electrical issues.
Common thought process usually focuses on the positive side of the circuit when the negative side is equally important but harder to follow if you don't have a correct specific diagram...
Is it possible that only one or two coils made the others look bad?
I had a cam solenoid issue on one bank, but got misfires on all 6 because the engine was just having trouble managing fuel and timing (presumably). I wonder if a bad coil could cause misfires on more than 1 cylinder.
Yeah...exactly what I was trying to get at when I wrote :
"
I guess I just don't know enough about how the ignition system/ECU works - maybe one coil misfiring causes the others to misfire as well..."
Clearly, without a ground you have no circuit ! Without a good/clean ground, you have an intermittent circuit. The ground is the "redheaded stepchild" of electricity/electronics - just as important as voltage/current but often overlooked...
I suspect the reason is because these Porsches are very reliable, so when there IS a problem, we tend to think a part/component has failed, but because most parts are quite reliable, the connections become the failure point. Just a guess though...
I also think that intermittent problems that affect communication are scenarios that haven�t been tested on the lab all that well.
What do �they� say? That 90% of the world�s problems are communication problems? When it comes to computers and electrical circuits, intermittent issues can often produce the strangest of symptoms.
Anyway, I�m glad you got this resolved - good for you - being prudent and seeing it through.
Got it. Last ground problem I had was on a 1964 Triumph TR4 back in 1970 and was wondering. BTW it was a lot easier to find a grounding problem on the 1964 Triumph than these cars!
My Dad had a Triumph Spitfire back in the late '60's/early '70's (it was a mid/late '60's model). It was a great car when it was running...
Those things were notorious for electrical/mechanical gremlins...
Glad you got it sorted.
I missed it but hw many miles on the new motor when this started?
I'm getting ready to ship (old motor) mine out and can't wait!
Yeah I got stopped by the police one night because my taillights were not working. I got out opened the hood and jiggled the terminal board and the taillights along with the gauge lights came back on. Cop said ok get that fixed but gave me a ticket for no license plate light! Previous owner had removed the rear bumper uprights that apparently also contained the license plate light! I ended up hole sawing a hole in the trunk lid and installing a light. Things were much easier back then...in so many ways.
My 1986 944 had really high quality copper ground rings for a multitude of circuits. Unfortunately, many of those nice copper ground rings landed on aluminum grounding lugs. Not a good situation after a couple of decades or more. As we all know now, copper and aluminum don�t play together well for long periods of time. I spent several hours on a weekend cleaning up all the lugs. It made a big difference...electrical gremlins disappeared....at least for another decade or so.
Hello,
For the last 6 weeks I was trying to figure out why I was getting misfires. They were very rare, like every 8 times I drive it and usually it was when first starting the motor. After a short warm up, the car usually would run better. Last weekend the misfires were enough so that I didn't want to run the car. Motor has 6k miles and plugs and coils were new one year ago. Bought new MAF. Didn't help. replaced cylinder 5 coil with an older but known good coil. Didn't help. Took car to the shop that had swapped my motor last year and they were able to sort it out. They smoke tested for vacuum leaks, swapped coil with cylinder 6, misfires stayed on cylinder 5, compression tested the cylinder, 185PSI. Finally they replaced the cylinder 5 fuel injector. No more misfires. All six injectors were bought new last year.
Wow. I have heard from Jake and others that injectors are a very important part of a healthy engine. And that rebuilt injectors are not always rebuilt to a perfect specification.
Good to know.
Exactly, he's mentioned it many times where rebuilt injectors didn't perform any better after cleaning. While the gunk can be removed, the internal wear is still a factor which produces a poor spray patterns. In most cases, it's wise to put the money into brand new injectors.
No, it was freshly rebuilt engine. Moved all my parts to the new engine. My original engine had 95k and had some pretty bad scoring that I had been nursing for 35k miles. Eventually I was using a quart of oil every 1000 miles and I am pretty sure my cats were getting ruined. It first started ticking a bit around 60k. I had the car a year at the time and bought it with 47k miles.
Otherwise, I gave the shop a bunch of new parts to replace while swapping. Clutch kit, slave cylinder, AOS, Fabspeed mufflers, cheap(but new) cats. some vacuum hoses that are hard to reach while engine is in. New plugs, new fuel injectors, new coolant expansion tank, and a few other things I could think of. The fuel injectors where new Bosch white injectors for around $35 each. I wonder if they were refurbished?
Where did you get the Bosch injectors? Come with the rebuilt engine? Or some you found?
Unless you have an itemized list, the term "rebuild" could mean anything. I wouldn't worry over it at this time. I would just keep a close eye on anything that may pop up. The phantom misfire could have been the injector or it could be something else. Lots of things could cause misfires.
I bought all the extra parts on my own from pelican parts, rock auto for some stuff etc. The engine was rebuilt long block with lots of pics as it was assembled. So I am pretty confident about where everything came from. There were a few gaskets and different bolts, a crankshaft pos sensor that broke when removing. My shop said almost every bolt they removed from my old engine snapped etc. Ugh. Since I got the new engine installed, I personally replaced alternator, water pump with pier burg and two O2 sensors up and downstream on bank 1. Otherwise nothing major until I couldn't figure out he misfires. But the only thing that fixed it was the injector.
True, but they still got me for just under $1000. All the troubleshooting, compression test, smoke test, checking plugs and swapping coils etc. But I would've spent a bunch of money replacing all coils and plugs(that weren't actually the problem). From what I understand, injector replacement is harder than coils and plugs. I have done coils and plugs a few times but it isn't that much fun. I have a durametric and could've watched misfires in real time but i really didn't want to suffer through it all. Sometimes spending the money is easier than trying to sort it out. I save so much money doing my own brakes on the 6 cars we have as well as other easy stuff like oil changes. I am sure the shop would have charged me a good amount if I had them replace my alternator and water pump. I also replaced my heater core, not too hard and I replaced my window cowl and one wiper spray nozzle.
Now I just need to fix my passenger window regulator and my cruise control. Although, I rarely use cruise control in any car.
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